unber - ASN.1 BER Decoder

unber [-1] [-iindent] [-p] [-tdata-string] [-] [infile...]

unber takes the BER-encoded files and dumps their internal structure as human readable text. A single dash represents the standard input. (The DER and CER formats are both subsets of the BER, and are also supported.)

-1

Do not attempt to read the next BER structure after the first one. This may be useful if the input contains garbage past the single BER sequence. By default, unber continues decoding until the end of file (input stream).

-i indent

Use the specified number of spaces for output indentation. Default is 4 spaces.

-p

Do not attempt pretty-printing of known ASN.1 types (OBJECT IDENTIFIER, INTEGER, BOOLEAN, etc). By default, some ASN.1 types are converted into the text representation. This option is required for enber(1).

-t data-string

Interpret the data-string as a sequence of hexadecimal values representing the start of BER TLV encoding. Print the human readable explanation.

unber dumps the output in the regular XML format which preserves most of the information from the underlying binary encoding.

The XML opening tag format is as follows:

<tform O="off" T="tag" TL="tl_len" V="{Indefinite|v_len}" [A="type"] [F]>

tform

Which form the value is in: primitive ("P") or constructed ("C") or constructed with indefinite length ("I")

off

Offset of the encoded element in the unber input stream.

tag

The tag class and value in human readable form.

tl_len

The length of the TL (BER Tag and Length) encoding.

v_len

The length of the value (V, encoded by the L), may be "Indefinite".

type

Likely name of the underlying ASN.1 type (for UNIVERSAL tags).

[F]

Indicates that the value was reformatted (pretty-printed). This may only appear in the output as long -p command line option is not specified.

Sample XML output:

<I O="0" T="[UNIVERSAL 16]" TL="2" V="Indefinite" A="SEQUENCE">
  <P O="2" T="[UNIVERSAL 19]" TL="2" V="2" A="PrintableString">US</P>
  <C O="6" T="[UNIVERSAL 16]" TL="2" V="11" A="SEQUENCE">
    <P O="8" T="[UNIVERSAL 2]" TL="2" V="4" A="INTEGER" F>832970823</P>
  </C T="[UNIVERSAL 16]" A="SEQUENCE">
</I O="14" T="[UNIVERSAL 16]" A="SEQUENCE">

Decode the given Tag/Length sequence given in hexadecimal form:

    unber  -t "bf 20"

    unber  -i 2   filename.der

    cat ... | unber -

    cat ... | unber -p - | enber - > filename.ber

The constructed XML output is not necessarily well-formed.

When indefinite length encoding is being used, the BER sequence, which is not terminated with the end-of-content octets, will cause the terminating </I> XML tag to disappear. Thus, the invalid BER framing directly causes invalid XML output.

The enber(1) utility understands this convention correctly.

enber(1), asn1c(1)

Lev Walkin <vlm@lionet.info>